1. Technical Field
This disclosure generally relates to surface emitting laser diode, surface emitting laser array, optical scanning device and image forming apparatus, and more particularly to a surface emitting laser diode emitting a laser beam in a direction perpendicular to a substrate, a surface emitting laser array including a plurality of such surface emitting laser diodes, an optical scanning device having such a surface emitting laser array, and an image forming apparatus having such an optical scanning device.
2. Description of the Related Art
A surface emission laser diode of vertical cavity surface emission laser (VCSEL) structure is a laser diode that emits light in a direction perpendicular to a substrate and draws attention these days in view of its advantageous features of low cost, low power consumption and compact size as compared with the laser diode of edge emission structure that emits light in a direction parallel to the substrate. Further, such a surface emission laser diode of VCSEL structure has high performance and is suitable for constructing a two dimensional device.
The laser diode of VCSEL structure can be used for example for the optical source used for optical writing in printers, or the like, the optical source used for optical writing in optical disk apparatuses (oscillation wavelength: 780 nm; 850 nm), and the optical source for optical transmission systems such as LAN (local area network) that uses optical fibers (oscillation wavelength: 1.3 um; 1.5 um). Further, it is thought promising to use such a surface emission laser diode for the optical source of optical transmission between circuit boards, between devices inside a circuit board, between chips forming an LSI (large scale integrated circuit), and between the device elements inside an LSI.
It is desirable for the optical source for optical transmission systems to emit single wavelength and high output power.
Further, it is desirable for the optical source for optical writing in optical scanning apparatus of image forming apparatus to have stable polarization direction.
For example, each of Japanese Patent No. 3697903, Japanese Laid-Open Patent Application No. 2001-284722, IEEE Photonics Technology Letters, Vol. 11 (1999) Pp. 1536-1538 and IEEE Photonics Technology Letters, Vol. 16 (2004) Pp. 368-370 proposes a configuration of a surface emitting laser diode for performing single transverse mode emission and high power output. However, such surface emitting laser diode has a trench installed on the top surface which emits in single transverse mode.
A surface emitting laser diode was proposed in Proceedings Symposium IEEE/LEOS Benelux Chapter, 2002, Amsterdam, Pp. 103-106, having a concavo-convex shape formed on a top surface of the surface emitting laser diode and such shape has shape anisotropy in direction perpendicular to emission direction. The surface emitting laser diode has single transverse mode, high power and stabilized polarization direction.
Controlling polarization direction is known by using inclined substrate.
However, even if the conventional technologies are combined, it is difficult to manufacture surface emitting laser diode having single transverse mode, high power, stable polarization direction, isotropic cross sectional shape of output beam and small divergence angle with high productivity.